The present invention relates to wastewater treatment facilities. More particularly, the present invention relates to modular wastewater treatment apparatus for treating wastewater while reducing the amount of sludge produced per unit of wastewater treated.
Conventional wastewater treatment facilities are large complexes for handling tens of millions of gallons of wastewater annually. These facilities produce clean water, yet also produce significant volumes of solidified waste sludge. Disposal of the waste sludge requires handling and disposal such as in landfills or other sources.
In a typical wastewater treatment plant, the influent passes through a series of treatment processes to remove large objects and then reduce the solids and waste particles before separating residual solids from the water. A headworks provides screening and grit removal. Screening removes roots, rags, cans and large debris from the flow of influent. A low-flow section facilitates removal of grit and heavy particulates. Primary treatment includes pre-aeration with air to freshen the wastewater and help remove oils that form scum on an upper surface of the water. This primary treatment accordingly combines sedimentation and floatation in order to remove settleable and floatable materials. Thereafter, secondary treatment removes suspended and dissolved solids. The secondary treatment typically involves treatment of wastewater with activated sludge in which biologically active microorganisms assimilate waste materials. Subsequently, disinfection kills pathogenic organisms in the clarified wastewater. The resulting effluent is then generally discharged to surface waters.
In treatment facilities that use activated sludge for wastewater treatment, raw wastewater is mixed in a first aeration tank with return activated sludge. This activated sludge typically comprises relatively high concentrations of biologically active microorganisms. These organisms consume the waste products to reduce the volume of solids in the wastewater. The term xe2x80x9creturn activated sludgexe2x80x9d comes from the source of such, a secondary clarifier, in which the microorganisms become highly concentrated. In the secondary clarifier, microorganisms and waste collect into large clumps of material known as floc. Activated sludge floc separates from the water by gravitational force and sinks towards a bottom portion of the secondary clarifier. A portion of the activated sludge is returned to the first aeration tank for mixture with raw highly concentrated influent wastewater. Finally, the separated clear water is removed to a disinfecting tank for disinfection and subsequent discharge with microorganisms to surface waters.
Activated sludge is typically measured in terms of biochemical oxygen demand (BOD) in terms of milligrams per liter (mg/l). This measures the strength of the wastewater and the primary food source for the microorganisms. The clarity of the wastewater is also evaluated in terms of total suspended solids (TSS). Domestic wastewater typically is about 250 mg/l BOD and 200 mg/l TSS. However, return activated sludge solids concentrations typically ranges between 2000 and 6000 mg/l TSS. Plant effluent is typically 10 mg/l for both TSS and BOD.
Periodically, the accumulated sludge is discharged to a dewatering facility such as a sludge lagoon or a drying bed. My U.S. Pat. No. 5,536,420 describes a vertical drainage drying bed for waste sludge. Drying beds in accordance with that invention significantly reduce the time required to remove excess water from the sludge. Dried sludge is removed from the drying bed with heavy equipment and may be used as a low-grade fertilizer.
While large scale water treatment facilities have met the need for major metropolitan areas to satisfactorily treat wastewater prior to discharge to streams and lakes, these large scale facilities are significantly expensive. In recent years, environmental concerns have increased the regulatory oversight and rules governing wastewater treatment and discharge. Smaller communities are now finding it imperative that wastewater be treated prior to discharge into streams and rivers. Natural percolation of wastewater is no longer satisfactory. However, the expense of construction and operation of large scale wastewater treatment facilities has significantly increased the costs of such.
Accordingly, there is a need in the art for an low capacity modular wastewater treatment apparatus. It is to such that the present invention is directed.
The present invention meets the need for an improved modular wastewater treatment facility by providing an integrated vertical wastewater treatment apparatus for placement as a modular unit on a land site to treat influent wastewater. The modular apparatus comprises a vessel having a closed bottom and an open upper end. The lower portion of the vessel defines an aeration zone for receiving a flow of influent wastewater with suspended solids for sanitary treatment. The influent wastewater communicates from an inlet through a mixing chamber into the aeration zone. A plurality of nozzles disposed within the aeration zone communicate with a supply of low-pressure air for injecting oxygen into the aeration zone to facilitate biological digestion of the suspended solids in the wastewater for sanitary treatment and the conversion of the suspended solids into activated sludge. An airlift has an inlet at a first end that communicates with a portion of the aeration zone in which the activated sludge gathers in concentration. The airlift has an outlet at a second opposing end. The airlift communicates with a supply of pressurized air to create a flow of concentrated activated sludge by a plurality of air bubbles moving from an air inlet through an uplift tube of the airlift. The mixing chamber in the vessel receives the flow of the wastewater with the suspended solids from the inlet and the concentrated activated solids from the aeration zone from the uplift tube. A secondary clarifier in a portion of the vessel superior to the aeration zone receives a flow of wastewater and sludge from the aeration zone by influence of the plurality of air bubbles introduced through the nozzles in the aeration zone. The secondary clarifier comprises a pair of opposing baffles and each baffle has a sludge receiving plate disposed at an oblique angle relative to the respective baffle and downwardly extending towards the opposing baffle to define a gap between lower distal end portions through which the wastewater and activated sludge flow into the secondary clarifier. One of the receiving plates extends past the opposing receiving plate to define a threshold to the secondary clarifier. The baffles cause a stilling of the wastewater in the secondary clarifier while the sludge deposits settlingly on the receiving plates where it accumulates and falls by mass into the aeration zone, resulting in treated water separated from the activated sludge. A trough disposed in the secondary clarifier for receives treated water separated from the sludge in the secondary clarifier which treated water communicates through an outlet outwardly of the treatment apparatus.
In another aspect, the present invention provides a method of treating sanitary and industrial wastewater in an integrated vertical-processing apparatus placed as a modular unit on a land site, comprising the steps of:
(a) providing through an inlet a flow of influent wastewater having at least suspended solids for sanitary treatment into an aeration zone in a lower portion of a vessel having a closed bottom and an open upper end;
(b) injecting a plurality of air bubbles through a plurality of nozzles disposed in the aeration zone, the nozzles communicating with a supply of low-pressure air to facilitate biological digestion of the suspended solids in the wastewater for sanitary treatment and the conversion of the suspended solids into activated sludge;
(c) communicating a flow of concentrated activated sludge and wastewater from a portion of the aeration zone in which the activated sludge gathers in concentration through an airlift having an inlet at a first end therein and an outlet at a second opposing end, the airlift communicating with a supply of pressurized air to create the flow of concentrated activated sludge by a plurality of air bubbles moving from an air inlet through an uplift tube of the airlift;
(d) introducing into the mixing chamber the concentrated activated solids from the aeration zone from an outlet of the uplift tube, whereby the activated solids mix with the influent wastewater;
(e) communicating the wastewater and the activated sludge to a secondary clarifier in a portion of the vessel superior to the aeration zone by influence of the plurality of air bubbles introduced through the nozzles in the aeration zone, the secondary clarifier comprising a pair of opposing baffles and each baffle having a sludge receiving plate disposed at an oblique angle relative to the respective baffle and extending towards the opposing baffle to define a gap between lower distal end portions for the wastewater and sludge to flow into the secondary clarifier, with one of the receiving plates extending past the opposing receiving plate to define a threshold to the secondary clarifier, the baffles causing a stilling of the wastewater in the secondary clarifier with the sludge being deposited settlingly on the receiving plates where it accumulates and then falls by mass into the aeration zone, resulting in treated water separated from sludge; and
(f) communicating treated water separated from the sludge in the secondary clarifier to an outlet.